It has long been recognized that the operational efficiency of a variety of engines, including turbines, can be increased by increasing the temperature at which they operate. Thus, every effort is made, within practical limits, to increase such temperatures. However, as is the case with a large variety of efforts towards improvement in untold numbers of fields of endeavor, various trade-offs must be made.
That is to say, while substantial increases in operating temperatures of engines can be achieved through the use of exotic materials capable of withstanding those temperatures, such a realization of improved operating efficiency may be of little practical value where the cost of the exotic materials is such as to make their employment impractical from the economic standpoint. Consequently, lower cost materials less capable of withstanding high temperatures are frequently employed and the temperatures reduced even though this may mean a greater consumption of fuel and/or a shorter engine life.
Achieving increased operational temperatures for turbine engines is particularly difficult in turbine engines of the so-called "monorotor" type. Engines of this type typically include an essentially one-piece rotor with one side defining a radial outflow compressor and the opposite side defining a radial inflow turbine wheel. This construction is extremely compact in that the cooling effect of air on the compressor side readily absorbs heat through the rotor that is applied to the same on the turbine side, allowing the use of higher operating temperatures. However, other, non-rotor parts of the engine, are subject to various problems as a consequence of this type of construction. For example, the rear engine shroud, which typically supports the turbine nozzle blades along with the front turbine shroud is always subjected to hot gases, either on the combustor side thereof or on the turbine wheel side thereof, or both. In contrast, the front engine shroud is subjected to relatively cool gas exiting from the compressor and, of course, the interconnecting vanes of the turbine nozzle conduct substantial heat to both.
In any event, while the front turbine shroud and at least those ends of the vanes in thermal conductive relation therewith run relatively cool, the rear engine shroud does not, which results in warping. As a consequence, the turbine nozzle blades may crack and shroud burnouts occur with undesirably high frequency.
The present invention is directed to overcoming one or more of the above problems.